Process of producing water-repellent gypsum sheathing board



Patented July 10, 1951 PROCESS OF PRODUCING WATER-REPEL- LENT GYPSUMSHEATHING BOARD Thomas P. Camp,

Arlington Heights, 111., assignor to United States Gypsum Company,Chicago, III., a corporation of Illinois No Drawing. Application May 10,1946, Serial No. 668,785

3 Claims. (Cl. l54=-86) The present invention relates to improvements inwaterproof and water-repellent gypsum sheathing board.

The invention relates more particularly to that type of gypsum sheathingboard in which the fibrous cover sheets are rendered water-repellent bythe expedient of causing the fibers of the cover sheets to adsorba.water-repellent soft hydrocarbonaceous material, for example,petrolatum or petroleum jelly.

The invention further relates to a gypsum sheathing board comprising aset core of gypsum, the individual crystals of which are coated with awater-insoluble and water-repellent coating consisting either ofparaflln alone or composition comprising both asphalt as well asparaflin, and having at least one of the cover sheets renderedwater-repellent.

One of the objects of the present invention is the production of asheathing board having the usual set gypsum core which has been maderesistant to and repellent to water by the incorporation therein, duringits manufacture and while still in the state of a slurry, of a fusibleorganic waterproofing material, the core being enclosed by and adheredto strong cover sheets which have been integrally sized with rosin sizeand which have been previously or subsequently coated with a highlyhydrophobic coating which is applied to the individual fibers of thecover sheets, leaving, however, the normal interstices intact.

A further object of the invention is to produce a waterproof sheathingboard having a gypsum core and a highly water-resistant surface which,however, is still vapor-permeable.

A further object is to produce water-repellent cementitious boardsprovided with highly waterproduct, I have described one valuable andemcient method of preparing the gypsum core for I a sheathing board. Ihave found that the prodproof and water-repellent paper liners, inwhichboards the cementitious core has been rendered water-resistant by thepresence therein of a waxy material, but which core can still be driedso as toremove excess water without the necessity of employingexcessively high drying temperatures.

One of the serious disadvantages of gypsum sheathing board in the pasthas been its lack of water resistance when exposed to the elements. Avery particular disadvantage was the softening action of the exposedcore when moistened with water. This frequently occurred during periodsof wet weather when a gypsum sheathing board was exposed in piles at thesite of a building operation prior to erection of the board. In acompanion application, Serial No. 585,791 now Patent No. 2,432,963, fora water-resistant gypsum uct described in that application can befurther improved by treatment of the exterior surfaces of the sheathingboard to make them extremely hydrophobic to water. It is advisable thatthe surface liners of the gypsum sheathing not only be water resistant,but the surface of the liner should not be easily wetted by water. Inother words, it should have a negative capillary effect so that waterwill rapidly run oil the surface. I have discovered that this can bemost efliciently and cheaply accomplished by coating the paper linersused for manufacture of the sheathing with petrolatum, which is alsoknown as petroleum jelly.

The paper liners used on both sides of the waterproof gypsum core,thereby forming the sheathing board, are made from chip papers, usuallyfrom reworked waste papers, which in their re-formation are heavilysized with rosin size, thereby making them highly water resistant. Thesepapers are usually made in thicknesses of .020" to .030" and weigh about-75 pounds per thousand square feet, and while highly water resistant,nevertheless have a suiilciently open texture so that they will bondcompletely and satisfactorily with the gypsum core, which usuallycontains from about 5 to about 10 pounds of farinaceous material perthousand square feet of board.

The application of the water-repellent material, for instance,petrolatum, preferably may be made at the paper machine during theformation of the paper. The best practice is to apply ordinarypetrolatum in a liquid state, at a temperature of F. to F., to theoutside liner of the paper on the calender stack, using the water boxeswhich are provided for such calender stacks to serve as the tank supplyfrom which the petrolatum is drawn. Paper of the aforesaidspecifications will absorb from about 5 to about 10 pounds of heatedpetrolatum per thousand square feet of paper at ordinary machine speeds,which amount is found to be highly satisfactory and sufiicientlywater-resistant for the purpose. Instead of applying the petrolatum onthe calender stack, it may be applied to the paper subsequent to itsmanufacture by an ordinary paper coating machine.

When preparing the liner paper employed for the manufacture of gypsumsheathing board at the paper mill, as above described, I find that v thepetrolatum coating will be most uniformly distributed over the surfaceof the paper, and after the paper has stayed in storage a week or morethe petrolatum will have thoroughly diffused throughout the paper fromthe front to the back, but while the petrolatum has completelypenetrated the paper, nevertheless it will be found that the bond of thegypsum core tothe coated paper liners is not impaired, even though bothsides of the paper liner show a marked hydro phobic effect. This isquite an unexpected result, inasmuch as oils and waxes of most anyorigin will interfere with the proper bonding of gypsum slurries toother surfaces. The oils and waxes, acting usually as a continuous film,are thereby eflicient parting agents preventing bond between the gypsumsurface and other surfaces of any type. I would explain this unusual andunexpected result and effect of bonding between the gypsum and thehydrophobic paper liners as being due to the fact that there is nocontinuous film of petrolatum. That is to say, the interstitial porositybetween fibers remains substantially intact and the petrolatum has beenabsorbed by the fiber itself without bridging the spaces or voidsbetween fibers, thus enabling the gypsum slurry to effect a mechanicalbond through the interstitial spaces with the irregular surfaces of thefibers themselves.

Usually this bond is the result of re-crystalization of the calcinedgypsum used for producing the board core into the form of calciumsulfate dihydrate which latter material has a tendency to form longneedle-like crystals. These crystals are interlaced in the core, but agreat many of them penetrate into the interstices of the cover sheets,thereby mechanically interlocking the cover sheets with the core, thusproducing a very strong bond. This bond is further protected by thepresence of some form of cooked carbohydrate, such as cooked starch, inthe core material, which farinaceous material, during the drying oftheboard, migrates to the interface between the core and the coversheets, thereby surrounding the gypsum crystals at this critical point;therefore, when the board is dried after the core material has set, thedrying being at temperatures which would normally re-calcine the gypsum,the crystals are protected from recalcination by this farinaceouswater-holding layer. While it would not have been expected that a gypsumcore could be made to bond on waterproof paper, I have found that,contrary to this expectation, paper containing the amounts of petrolatumor similar soft hydrocarbonaceous material will nevertheless bond,undoubtedly due to the fact that the interstices of the papers have notbeen appreciably impaired by the treatment with the water-repellentmateria1.

Moreover, during the drying of the board, the vapor formed from theresidual water in the boards may escape through the cover sheets bypassing in vapor form through the interstices of the otherwisewater-repellent cover sheets. The fact that the individual fibers of thecover sheets are not wettable by water prevents physical water frompenetrating through these sheets, mainly because the porosity isovercome by the negative capillarity of water relative to the petrolatumcoated fibers.

I have found such paper liners to perform very satisfactorily on thegypsum sheathing forming machine, and subsequently to go through thedryers at high temperatures without blowing. blistering or otherwisedisturbing the sheet and without appreciably retarding the rate ofmoisture elimination from the core, which is highly important in theproduction of such products. I find that while the porosity of theliners is reduced somewhat and conversely the vapor resistance of thefinished sheathing is increased, neither of those values is suflicientlyaltered to markedly interfere with the characteristics of the finishedsheathing.

Gypsum sheathing made in accordance with the present invention is highlywater-repellent and may therefore be freely used in place of ordinarywooden sheathing.

I have not deemed it necessary to describe in detail the manufacture ofa suitable gypsum core or the details of the manufacture of the gypsumsheathing board, as all this is carried out in machinery which is wellknown in the art, and fully familiar to gypsum board manufacturers andproducers. The core consists of calcined gypsum in admixture with theproper amounts of retarders and accelerators, fibers, and-usually alsoof a foam which advantageously may be made from a low viscosity starchcontaining a suitable foam producing agent. Such a method of making aboard is fully described in my Patent No. 2,207,339, and the manufactureof a suitable water-repellent gypsum core board is also shown and fullydescribed in the patent to King and Camp No.'2',19 8, 776, and in myalready mentioned patent No. 2,432,963.

Reserving to myself such equivalents as will occur to those skilled inthe art into which this application falls, I claim as my invention:

1. Process of producing water-repellent gypsum sheathing board whichcomprises impregnating heavy paper with an amount of petrolatuminsufficient to close the interstices of said paper, and thereafterapplying a slurry of calcined ypsum thereto which upon eventual settingwill bond itself to the thus treated paper.

2. Process of producing water-repellent gypsum sheathing board whichcomprises applying to one side of a heavy sheet of paper an amount ofpetrolatum insuflicient to close the interstices thereof, storing thethus treated paper to permit diffusion of said petrolatum through to theother side of said paper, and thereafter applying a slurry'of calcinedgypsum thereto, which upon eventual setting will bond itself to the thustreated paper.

3. Process of producing water-repellent gypsum sheathing board whichcomprises impregnating heavy paper with melted petrolatum in an amountof from about 5 to 10 pounds per 1000 square feet thereof, therebyrendering it waterrepellent but not vapor resistant; thereafter placinga slurry of calcined gypsum containing water-proofing agents disposedtherein between two layers of said thus treated paper; and drying theresulting laminated structure.

THOMAS P. CAMP.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,295,466 Farmer Feb. 25, 19191,325,883 Sexton Dec. 23, 1919 1,784,993 Mason Dec. 16, 1930 1,793,810Sexton Feb. 24, 1931 1,903,787 Lodge Apr. 18, 1933 2,319,116 Dodge May11, 1943 Certificate of Correction Patent No. 2,560,521 July 10, 1951THOMAS P. CAMP It is hereby certified that error app-ears in the printedspecification of the above numbered patent requirlng correction asfollows:

Column 4, line 29, for No. 2,198, 776 read No. 2,198,776; line 58, forthe word disposed read dispersed and that the said Letters Patent shouldbe read as corrected above, so that the same may conform to the recordof the case in the Patent Ofiice. Signed and sealed this 4th day ofSeptember, A. D. 1951.

THOMAS F. MURPHY,

Assistant Oommz'ssioner of Patents.

3. PROCESS OF PRODUCING WATER-REPELLENT GYPSUM SHEATHING BOARD WHICHCOMPRISES IMPREGNATING HEAVY PAPER WITH MELTED PETROLATUM IN AN AMOUNTOF FROM ABOUT 5 TO 10 POUNDS PER 1000 SQUARE FEET THEREOF, THEREBYRENDERING IT WATERREPELLENT BUT NOT VAPOR RESISTANT; THEREAFTER PLACINGA SLURRY OF CALCINED GYPSUM CONTAINING WATER-PROOFING AGENTS DISPOSEDTHEREIN BETWEEN TWO LAYERS OF SAID THUS TREATED PAPER; AND DRYING THERESULTING LAMINATED STRUCTURE.